The Collaborative International Dictionary of English v.0.48:

Posy \Po"sy\, n.; pl. Posies. [Contr. fr. poesy.]
   1. A brief poetical sentiment; hence, any brief sentiment,
      motto, or legend; especially, one inscribed on a ring.
      "The posy of a ring." --Shak.
      [1913 Webster]

   2. [Probably so called from the use of flowers as having an
      enigmatical significance. Wedgwood.] A flower; a bouquet;
      a nosegay. "Bridegroom's posies." --Spenser.
      [1913 Webster]

            We make a difference between suffering thistles to
            grow among us, and wearing them for posies. --Swift.
      [1913 Webster]

WordNet (r) 3.0 (2006):

posy
    n 1: an arrangement of flowers that is usually given as a
         present [syn: bouquet, corsage, posy, nosegay]